Executed by charging down-backward then pressing forward and kick, Vega employs his backflip animation as an offensive attack. It breaks armor in more recent appearances.
The forward distance and amount of strikes are determined by the kick button pressed: light kick version has Vega do a single strike in a very short hop; medium and heavy kick versions both strike twice, with heavy kick covering a bigger distance.
The EX Special introduced in Street Fighter IV executes with the same speed as the heavy kick version, has Vega jump much higher, increased damage and stun values, and slightly bigger interval between the two hits.
As with all anti-air moves, it works well for punishing or inhibiting incoming air attacks, though Vega will be left vulnerable if it whiffs or gets blocked. Scarlet Terror is a backflip that can be used as an anti-air but it is also useful to punish opponents who like to use Focus Attacks, either to actually attack or just to feint, up close. It can also be used as Vega is getting up to avoid some of the opponent's wake-up strategies.
If the opponent is hit with an anti-air light kick version Scarlet Terror, the player can follow it up with an EX Scarlet Terror for increased damage.
The EX version works best as an anti-air, and should be the preferred version to use if Vega is getting up from a knockdown.